APL3208B datasheet(11/17 Pages) ANPEC

11 / 17 page

Rev. A.2 - Nov., 2009

APL3208A/B/C

www.anpec.com.tw

Application Information

BAT Selection

Connect the VBAT pin to the positive terminal of battery

through a resistor R

BAT for battery OVP function. The RBAT

limits the current flowing from VBAT to battery in case of

VBAT pin is shortened to ACIN pin under a failure mode.

The recommended value of R

BAT is 200kΩ. In the worse

case of an IC failure, the current flowing from the VBAT

pin to the battery is:

(30V-3V)/ 200k

Ω =135µA

where the 30V is the maximum ACIN voltage and the 3V

is the minimum battery voltage. The current is so small

and can be absorbed by the charger system.

Capacitor Selection

The input capacitor is for decoupling and prevents the

input voltage from overshooting to dangerous levels. In

the AC adapter hot plug-in applications or load current

step-down transient, the input voltage has a transient

spike due to the parasitic inductance of the input cable. A

50V, X7R, dielectric ceramic capacitor with a value be-

tween 1

µF and 4.7µF placed close to the ACIN pin is

recommended.

The output capacitor of CHG_DET is for CHG_DET volt-

age decoupling. And also can be as the input capacitor of

the charging circuit. At least, a 1

µF, 10V, X7R capacitor is

recommended.

Layout Consideration

In some failure modes, a high voltage may be applied to

the device. Make sure the clearance constraint of the PCB

layout must satisfy the design rule for high voltage. The

exposed pad of the TDFN2x2-8 performs the function of

channeling heat away. It is recommended that connect

the exposed pad to a large copper ground plane on the

backside of the circuit board through several thermal vias

to improve heat dissipation. The input and output capaci-

tors should be placed close to the IC. The high current

traces like input trace and output trace must be wide and

short.

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